1. Field of the Invention
The present invention relates to an apparatus and a method for inspecting wiring on a circuit board, and more particularly it pertains to such circuit board inspection apparatus and method which inspect for any occurrence of a short-circuit and/or discontinuity of the wirings on the board. The present invention is applicable to inspection of wirings which are formed on various types of boards or substrates, such as printed circuit boards, flexible wiring films or substrates, multi-layer wiring boards, glass substrates for liquid crystal displays and plasma displays, and film carriers for semiconductor packages.
2. Description of Prior Arts
In general, a plurality of wirings are formed on a board in a wiring pattern. A number of wiring inspection apparatuses have already been proposed and marketed which are capable of inspecting whether a wiring pattern is finished as designed. In order to inspect, for example, whether mutually adjacent pair of wirings, sequentially selected from a group of wirings forming the wiring pattern, are short-circuited or not, a conventional wiring inspection apparatus presses a pair of conductive spring probes, electric terminals or the like (representatively referred to as probes) respectively against the selected wirings. A short-circuit condition between the selected pair of wirings is inspected by checking whether a predetermined current flows through the probes as a voltage is applied between the probes.
Such a short-circuit inspection is conducted usually after the wiring pattern is formed on the board by electroplating or other appropriate methods but before electronic parts are mounted on the board.
Immediately after a wiring pattern is formed, all the wiring paths of the wiring pattern are electrically connected to a temporary common wiring which is used for electroplating. Hence, it is not possible to perform a short-circuit inspection described above in this condition. To cope with this problem, a conventional method for wiring inspection employs a step of mechanically insulating the wiring from one another. In more detail, with reference to FIG. 21 a portion 11 is punched out of a board 1 together with wirings or wiring paths formed thereon to form an elongated opening and to separate the wirings 21 of a wiring pattern 2, e.g., seven wirings 21 from the common wiring or conductor 3 on the end of one side (i.e., the left-hand side in FIG. 21) of the wirings 21. Thus, the wirings 21 are electrically separated and insulated from one another. In this condition, seven conductive spring probes (FIG. 21 shows only four probes P1 through P4 for the simplicity of illustration) are pressed against ball grids or pads 22 respectively connected with the corresponding wirings 21 and disposed on the opposite surface of the board 1. Short-circuit inspection is carried out with a voltage being applied to sequentially selected pairs of the probes and electric current is detected therefrom. As to boards which are determined nondefective as a result of the short-circuit inspection, each extra portion of the board 1 is severed along a cutting line 12 (which is denoted at dashed-and-dotted line in FIG. 21), to finish the circuit board in a final shape.
The conventional short-circuit inspection of the wirings 21 as described above, requires a punching step for separating the wirings 21 from the common wiring 3 and thereby from one another. This additional step increases a cost for producing a printed wiring board. In addition, since it is necessary to ensure a additional area on the board 1 dedicated solely for the punching, an initial board size must be larger than the size of a final printed wiring board, thus even further increasing the production cost of the board. Moreover, recent design requirement for the wiring patterns of printed wiring boards, makes it impossible to leave or form a punch-through portion on the wiring boards as described above.
Thus, it would be an improvement if printed wiring boards could be inspected with the temporary common wiring 3 left unremoved. However, a wiring inspection apparatus or a wiring inspection method to enable such inspection has not been proposed to this date.
It is not only printed wiring boards which require the performance as described above, but glass substrates for liquid crystal displays and plasma displays as well may enjoy the merit of such procedure. That is, as a plurality of transparent electrodes are disposed on a glass substrate, it would be an improvement to inspect a wiring pattern of the group of transparent electrodes with the ends of the transparent electrodes electrically connected to each other.
The above operation also remains true as to film carriers for semiconductor packages. In a semiconductor package of a film carrier type, a plurality of wirings are arranged on a film carrier in conformity with the layout or arrangement of a semiconductor chip. Therefore, it would be an improvement to inspect a wiring pattern of the group of wirings with the ends of the wirings electrically connected to each other.
Further, for the purpose of improved productivity in the manufacturing of wiring boards, wirings are printed or deposited on a plurality of unit boards which are arranged contiguous in a plane one-dimensionally or two-dimensionally and integrated with each other. Where those unit boards are small or flexible, one can easily handle these boards if the boards are integrated into a somewhat large size during the formation of the wirings thereon and the inspection of their wirings. It is therefore effective to manufacture a wiring board with more than one of the unit boards integrated with one another and handled as one block.
FIGS. 22A and 22B show an example of a plurality of work pieces or unit boards WC (16 pieces in the example in FIG. 22A) which are integrated with each other in two dimensional arrangements as a work W. The work pieces will finally be separated from one another into eventually discrete unit pieces or boards, and are respectively incorporated in electric appliances or the like. Wiring processing such as plating, deposition and etching of wirings is performed on the integral work W. In this case, immediately after the wiring process, wiring patterns of the work pieces WC are connected to each other while wirings in each one of the work pieces are connected to each other. FIG. 22B shows an example of a circuit pattern formed on each of the work pieces WC.
When such a board or work W is to be inspected by the conventional method as described earlier, inspection is conducted on each of the work pieces WC after they are separated into discrete elements from one another. In the manufacturing, the work pieces are severed from each other and the wirings are separated from each other before the inspection of the wiring, and an integrated circuit chip and other circuit components are thereafter mounted on each work piece. However, the workability of the single work pieces WC is particularly poor when the work pieces WC are small or flexible. If the work pieces could be inspected while they are integrated with one another into a collective or unitary work piece, i.e., the condition just after the wirings are formed, their workability for the inspection will improve, and circuit components may be mounted respectively on the work pieces while they are integral with one another, thereby enhancing workability of the work pieces for the circuit component mounting.
Accordingly an object of the present invention is to provide a circuit board inspection apparatus which enables inspection of wirings or wiring paths on a circuit board while the wirings are electrically connected with one another on a common terminal.
Another object of the present invention is to provide a method for inspecting wirings or a conductive path on a circuit board while the wirings are electrically connected with one another.
Still another object of the present invention is to provide a circuit board inspection apparatus which enables inspection of wirings respectively formed on a plurality of circuit board units or work pieces while the units or pieces are integrated with one another with the wirings being electrically connected with one another.
Yet another object of the present invention is to provide a circuit board inspection apparatus for inspecting unexpected short-circuit and/or continuity of wirings or electric conductor patterns respectively formed on a plurality of board units or work pieces while the units and pieces are in a workable condition.
Further object of the present invention is to provide a circuit board inspection apparatus which inspects a plurality of circuit board units or work pieces efficiently.
Yet further object of the present invention is to provide a method for efficiently inspecting a plurality of circuit board units or work pieces while the units or pieces are integrated with one another with the wirings being electrically connected with one another.
Still further object of the present invention is to provide a circuit board inspection apparatus which has an effective and space saving structure for the inspection of wirings or a conductive path on a circuit board while the wirings are electrically connected with one another.
According to one aspect of the present invention, a magnetic field is supplied to the ends of the wirings that are electrically connected with each other and a magnetic flux of the magnetic field is caused to change with time, whereby an induced current flows between the wirings. The induced current is detected, and whether there is a short-circuit or disconnection in the wirings is judged based on monitoring of the detection result. Hence, it is possible to inspect the wirings with the ends of the wirings electrically connected with each other, which in turn leads to the following specific effects. That is, it is not necessary to perform a step, which is essential to inspections using the conventional wiring inspection apparatuses and conventional wiring inspection methods, of insulating between the wirings, and hence, a manufacturing cost is reduced. Further, it is possible to inspect whether there is a disconnection or short-circuit in such a board which can not be treated with this step.
According to another aspect of the present invention, when there are a plurality of same or different wiring patterns formed, whether there is a short-circuit or disconnection in wirings can be judged after positioning each wiring pattern relative to the magnetic field generation unit. Hence, it is possible to continuously inspect the respective wiring patterns one after another to find whether the wirings which form each wiring pattern are defective or not.
According to another aspect of the present invention, two wirings or wire paths are selected out of a wiring group or pattern which is formed by three or more wirings as an object wiring pair. A magnetic field is applied to the object wiring pair while a magnetic flux of the magnetic field changes with time, whereby an induced current flows through the object wiring pair. The induced current is detected, and whether there is a short-circuit or disconnection in the object wiring pair is judged. After judging, the test protocol is switched to a different object wiring pair. In a similar manner, application of a magnetic field to the new object wiring pair, current detection and judgment are performed with respect to all wiring pairs of the wiring group while sequentially switching between the wiring pairs. Hence, it is possible to inspect all wirings with the ends of the wirings of the wiring group still connected with each other.
According to still another aspect of the present invention, magnetic field applying means may comprise: (a-1) a core which is entirely formed by a conductive magnetic material and includes a first leg portion with a first end surface, a second leg portion with a second end surface and a link portion which links the leg portions to each other, the core being located on one side to the work, the first and second end surfaces of the core being faced respectively with the first ends of the wirings of different ones among work pieces; (a-2) a coil which is wound around the link portion; and (a-3) a magnetic path generation plate which is formed by a soft magnetic material, the magnetic path generation plate being disposed parallel to the work on the other side to the work so that a magnetic flux which exits at one of the end surfaces of the core is guided to the other one of the end surfaces of the core and a magnetic circuit is consequently formed. Since such magnetic field applying unit is used and since the magnetic field is applied simultaneously to the wirings, the following effect is obtained. That is, a signal is supplied to the magnetic field applying unit to thereby change the magnetic flux of the magnetic field with time, whereby an induced current flows through the wirings of the work pieces which face to the core. Based on the induced current, whether there is a short-circuit or disconnection in the wirings of the work pieces is judged, and hence, it is possible to efficiently inspect the wirings of the plurality of work pieces.